The present energy detect circuit is adapted for use in an autodialer/controller for facsimile equipment. Such a controller interconnects a facsimile unit with a standard telephone line. It may perform multiple poll and send commands at preprogrammed times of the day, thereby minimizing operator involvement.
Once the controller completes its connection to the intended remote receiving unit, it turns control over to the local facsimile unit.
Prior art autodialer/controllers do not include the ability to detect dial tones, busy signals or ring backs. Instead, they assume that a dial tone will be available or a WATS line available after dialing an access code. For example, when a prior art autodialer attempts to access a WATS line, it dials an access code and then waits a predetermined time before it continues dialing. It assumes that after the predetermined time the WATS line will be set up and not busy, and dials the number of the receiver it is to communicate with. If the WATS line is busy or is not set up, it still proceeds to attempt to complete the call. Obviously, the attempt is unsuccessful.
Similar problems are experienced with prior art autodialers which interface with a private branch exchange which requires a security code to be sent by the autodialer in order to gain access to a WATS or unrestricted telephone line.
It is desirous to be able to detect busy signals, dial tones and ring backs in order to control the operations of an autodialer. For example, if these signals could be detected, then an autodialer controlled by a microprocessor could dial the access code for a WATS line and wait until a dial tone is received prior to continuing to dial. If a busy signal is received, then the autodialer can wait a few minutes and attempt to access the line again. Similarly, the above mentioned problems with entering security codes could be eliminated.
An autodialer/controller which is responsive to dial tones, ring backs, and busy signals gives improved performance. Thus, it need not wait a predetermined time before dialing when a dial tone is available before the predetermined time elapses. Additionally, if a busy signal is detected, it will not attempt to turn control over to the facsimile system. Instead, it can be designed to redial the number until a connection is made and only then turn control over to the local facsimile equipment.
In order to implement the latter mentioned capabilities, an autodialer/controller may employ a programmed microprocessor which can execute commands programmed into it by a user. Thus, those skilled in the art will appreciate that it is quite feasible to program the microprocessor to dial a number and if a busy signal is detected, redial the number again in five minutes.
One problem that must be overcome in such a microprocessor controlled autodialer/controller is to prevent signals being transmitted onto a phone line from being confused with those being received from a remote PBX or other transmitter. Thus, the autodialer/controller must avoid interpreting signals it transmits as receive signals.
Another problem that must be overcome is the recognition of busy tones, dial tones and ring backs. Obviously, the programmed microprocessor cannot easily interpret these analog signals as they are received from the phone line. However, if these analog signals are translated into digital signals, the microprocessor can readily interpret which type of signal is being received.
Busy tones, ring back and dial tones consist of defined analog energy on-off patterns. These patterns are made up of analog signals having a specific power level and a specific bandwidth. By assuring that the signals meet the bandwidth and power levels, noise on the telephone line can be eliminated, leaving pure analog receive signals. If these signals are then transformed into a digital signal indicating the presence or absence of energy above a minimum power level and within the defined bandwidth, then this digital signal can be readily analyzed by the microprocessor to determine if a dial tone, busy signal, ring back, or some other signal is being received. For example, a dial tone is defined by the presence of continuous energy for greater than two seconds. Given a digital signal input indicating the presence of energy, the microprocessor can easily determine if continuous energy is present for at least two seconds. If it is, the microprocessor knows it has a dial tone and can proceed to dial the number it is programmed to access.
It is the general object of the present invention to overcome the drawbacks of the prior art by providing a circuit for use in a facsimile equipment controller which detects energy on a telephone line within the bandwidth and power range associated with signals transmitted from a remote PBX.
It is a further object of the present invention to provide a circuit for detecting energy on a telephone line which provides at its output a digital signal indicating the presence or absence of energy.
It is an additional object of the present invention to provide a circuit for detecting energy on a telephone line which utilizes CMOS circuitry that is driven by a single power supply.
It is another object of the present invention to provide a circuit for use in an autodialer for facsimile equipment which detects the presence of energy on a telephone line and additionally separates out receive signals.
These and other objects, features and advantages of the present invention will become more apparent from the detailed description of the preferred embodiment when read in conjunction with the drawings.